>In the form, I call mdc_main's GetByListId(), which fires the Hook methods. But when it gets to the hook methods, e.PrimaryKeyValue is undefined (null?), and causes them to bomb.

The business object raises an event before and after it does something "interesting". If you are looking at the primary key value at one of the "before" events, the primary key value may very well be null.

To get a closer look at what's happening in the parent business object you can set a breakpoint in mmBusinesObject.CallStateChange(). You can check the value of bizState as well as the primary key value.

Regards,